Taggants are materials, substances, molecules, ions, polymers, nanoparticles, microparticles, or other matter, incorporated into, onto or otherwise associated with objects for the purposes of identification or quantitation. More specifically, taggants are used in activities and products including but not limited to detection, analysis, and/or quantification measurements related to brand security, brand protection, trademark protection, product security, product identification, brand diversion, barcoding, grey market remediation, friend-or-foe analysis, product life cycle analysis, counterfeiting, anti-counterfeiting, forensic analysis of authenticity, authentication, biometrics, object tracking, chain-of-custody analysis, product tampering, anti-smuggling, smuggling detection, supply-chain tracking, product tracking, lost revenue recovery, product serialization, serialized authentication, freshness tracking, sell-by date tracking, use-by date tracking, and standoff detection/identification.
Taggants can be added to all forms of matter, including but not limited to solids, liquids, gases, gels, foams, semi-solids, glasses, plasmas, liquid crystals, amorphous and magnetically-ordered solids, superconductors, superfluids, Bose-Einstein condensates, and supersolids.
The addition of taggants to liquids, and in particular liquid hydrocarbons such as fuel, diesel oil, gasoline, kerosene, ethanol, biodiesel, methanol, crude oil, fuel additives, etc. has been described in the prior art, and is recognized to be useful for a number of reasons. Similarly, the addition of a taggant allows protection against counterfeiting, or use of the hydrocarbon in an improper setting (i.e. brand diversion). Likewise, the ability to measure the concentration of a taggant in a hydrocarbon allows a determination of purity: if the concentration is lower than added, it suggests that the sample has been tampered with (for example by addition of a less valuable hydrocarbon). Often, this tampering can be at the level of a 1-5%, so highly accurate and precise measurements of taggants are required. Measuring taggant concentration can also be invaluable for process monitoring, where crude oil (for example) is often mixed with mud, steam, water, and other impurities, and where knowledge of the actual oil concentration impacts how selected processes are carried out. In another example, when fuel products with different owners share the same infrastructure (e.g. a pipeline), a tagged fuel allows operators to know which fuel is at which location at which time.
Likewise, addition of a taggant also provides insurance against legal liability. For example, the absence of taggant in a spilled sample of oil or gasoline allows fuel owners who have added taggant to their oil or gasoline to be exempt from liability. In many cases, the use of known taggants results in insufficient precision, detection accuracy or other problems.
Many known methods of detecting taggants utilize one of several spectroscopic techniques, for example a surface-enhanced spectroscopy (SES) techniques such as SERS or SERRS. An extraordinarily large number of SERS-active materials exist. Broadly speaking, suitable materials fall in two categories: nano-/microscale and macroscopic. For example, certain sizes and shapes of Ag and Au nanoparticles, and aggregates thereof, are known to support SERS. Likewise, a large variety of macroscopic SERS substrates have been described in the literature, including electrodes, evaporated films, Langmuir-Blodgett films, 2-dimensional planar arrays, and so forth.
A significant weakness of previously-described SERS substrates is their inability to accommodate large sample volumes, and more particularly function well with very dilute analytes in large sample volumes. Consider, for example, a sample volume of 100 mls in water, containing a molecule to be analyzed at concentration of 10−15 M. The total number of molecules is 10−16 moles, or 60 million, which is a substantial number. Nevertheless, this poses a substantial problem for conventional SERS in that most macroscopic substrates are of dimensions of a few cm2 (or less), meaning the sample dimensions are large compared to the substrate dimensions. As a result, the number of molecules that come into contact with the substrate is very low per unit time, and even if there were irreversible adsorption, it may take hours to days for all molecules to reach the substrate surface.
Known prior art tagging methods which utilize SERS-active tags typically include a reporter molecule or dye with known SERS-active characteristics. For example, a known SERS-active chemical can be added as a dye to mark fuel and a subsequent SERS spectrum obtained when the SERS-active dye is associated with a SERS-active metal particle or substrate. Only a limited number of SERS active chemicals are known.
The present invention is directed toward overcoming one or more of the problems discussed above.